The phase position of the camshaft in relation to a crankshaft may be ascertained by a sensor wheel mounted on the camshaft. This sensor wheel has teeth, which are scanned by a Hall sensor, for example, when the camshaft rotates. Whenever the beginning of a tooth is detected, for example, a phase flank interrupt is triggered in an engine control unit. Sensor wheels having four teeth of different lengths are generally used on a camshaft. This special profile permits faster synchronization between the camshaft and the crankshaft and thus makes it possible to start the internal combustion engine more rapidly. As a special feature, such a sensor wheel also has four tooth flanks which are equidistant and with which an actual angular position of the camshaft is determined. A camshaft regulator sits in the actual angular position of the camshaft.
At low rotational speeds, for example, 1000 rpm, there is a new value for the actual angular position of the camshaft every 30 ms. If the phase position of the camshaft is to be adjusted rapidly, for example, with an adjustment period of less than 160 ms, then too few measuring points for the actual angular position of the camshafts are available accordingly. The speed of the camshaft between two phase flank interrupts is therefore determined and the actual angular position of the camshaft until arrival of the next phase flank interrupt is extrapolated linearly. In the case of changes in gradient of the phase position between the camshaft and the crankshaft in particular, severely overestimated or underestimated actual angular positions of the camshaft may be obtained with this method, which entails corresponding disadvantages for the control quality of the camshaft adjuster.
A sensor wheel having a larger number of teeth would trigger more phase flank interrupts per given time interval, which would require more computing capacity on the part of the engine control unit. The rapid synchronization between the camshaft and the crankshaft as achieved by a sensor wheel having four teeth of different lengths also could not be achieved with a sensor wheel having a large number of teeth.